The present invention relates to a semiconductor device and a method of manufacturing the same, particularly to technology that is effective when applied to a semiconductor device having a nonvolatile memory and a method of manufacturing the same.
As a nonvolatile semiconductor memory device capable of electrical write/erase, EEPROMs (Electrically Erasable and Programmable Read Only Memory) are used widely. These memory devices (memories) represented by flash memories widely used nowadays have an electroconductive floating gate electrode or a trapping insulating film surrounded by an oxide film, under the gate electrode of a MISFET, and utilize an electrical charge accumulation state in the floating gate and the trapping insulating film as storage information to read it as a threshold value of a transistor. The trapping insulating film means an insulating film capable of accumulating electric charges, and includes a silicon nitride film. Injection/release of electric charges to/from such an electric charge accumulation region shifts the threshold value of a MISFET to cause the MISFET to operate as a storage device. As the flash memory, a split gate type cell using a MONOS (Metal-Oxide-Nitride-Oxide-Semiconductor) film exists. This memory has, by using a silicon nitride film as the electric charge accumulation region, an advantage that the reliability of data retention is excellent because electric charges are accumulated discretely. Furthermore, because the reliability of the data retention is excellent, oxide films over and below the silicon nitride film can be thinned to enable low voltage write/erase operation, as compared with an electroconductive floating gate film.
Japanese Patent Laid-Open No. 2010-108976 (Patent Document 1) describes technology related to a split gate type nonvolatile memory, and describes, in paragraphs [0080] to [0082], formation of a gate insulating film GOX from a high-permittivity film.
Japanese Patent Laid-Open No. 2004-266203 (Patent Document 2) describes technology related to a nonvolatile memory element, and describes, in paragraphs [0138] to [0141], formation of a memory gate electrode 36 by an electroconductive film 35 made of a metal and has a resistance lower than a polycrystalline silicon film.